1. Field of the Invention
The present invention relates to a sensor for detection and monitoring of low/trace concentration fluid components, to a fluid processing apparatus and method utilizing same. The sensor apparatus and method of the invention have utility, inter alia, as an end point detector for the semiconductor manufacturing industry.
2. Description of the Related Art
In the conventional use of dry scrubbers, i.e., sorbent beds that reactively remove undesired components of gas streams flowed therethrough, it is critically important that the approach of the bed to exhaustion of its removal capacity thereof be accurately determinable. If the exhaustion of the removal capability of the bed is not detected by operating personnel, then gas requiring treatment will pass untreated through the bed and be passed to discharge, disposal or other process steps, still containing the components desired to be removed from such treatment effluent.
Such non-treatment, or inadequate treatment as the point of exhaustion is approached, may entail severe consequences. By way of example, dry scrubbers are used extensively in the semiconductor manufacturing industry, where the scrubber is employed to abate hazardous gases from the effluent from the processing plant, or specific operating components thereof. The failure to detect exhaustion of the scrubber bed thus may result in deleterious exposure of facility personnel to hazardous gases, as well as environmental contamination in the ambient surroundings of the semiconductor process facility. Additionally, incidents have been reported in which eductor devices downstream of scrubbers have experienced plugging when impurities have broken through the scrubbers without being detected.
Accordingly, it has been common practice either to require change-out of the scrubber bed, viz., replacement of the scrubber material in the bed with fresh scrubber medium, well prior to the actual exhaustion of the scrubber bed, i.e., with a substantial safety margin in respect of the operating life of the scrubber bed, or else to deploy monitors that detect actual or incipient breakthrough of the scrubbable components in the gas stream egressing the scrubber bed.
The first alternative, of change-out of the scrubber material well in advance of the exhaustion of the capacity of the scrubber bed, although effective in terms of preventing discharge of scrubbable components in the effluent gas, is inefficient in respect of the wastage of scrubber medium which could otherwise be employed to remove the scrubbable component, so that the effective capacity of the scrubber bed is not utilized. As a result, the scrubber bed must be oversized to accommodate the unused scrubber material.
The second alternative, of using monitors that detect actual or threshold breakthrough of the scrubbable components in the scrubber beds, is expensive, and involves the use of costly devices which additionally require significant maintenance (involving replacement of consumable elements, e.g., the frequent change of color tapes in so-called MDA monitors, or frequent change of cells in monitors such as those commercially available under the trademark Enmet), require inline recalibration not infrequently, and in some instances do not to measure the impurity species properly. In general, problems of cost, accuracy and reliability plague the existing commercially available monitors in application to scrubbing systems.
Another application in which the detection of low or trace concentrations of impurities is carried out is the monitoring of air or other ambient gases for the presence of trace hazardous gases. The systems currently commercially available such as the aforementioned MDA monitors or Kitagawa tubes, are either costly or else do not provide useful readouts. The MDA monitor is sensitive only down to concentration levels on the order of about 5 ppm, and readings below that level are inaccurate.
Accordingly it would be a significant advance in the art to provide a low cost, accurate, reliable, and easy fabricated and operated sensor device for monitoring of impurity species in fluid environments, such as gas steams discharged from a scrubber bed, or ambient gas environments which are menitored for the presence of contaminants.
It is another object of the invention to provide a highly sensitive and selective detection system for determining the presence of impurity species in fluid environments.
It is a further object of the invention to provide an end point detector for sensing the breakthrough of impurity species in such operations as dry scrubbing of process gases.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.